1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device of a thin film transistor (hereinafter referred to as “TFT”) type or the like and a manufacturing method thereof.
2. Description of the Related Art
A liquid crystal display device, in view of its characteristics that the device is thin, light-weighted and exhibits low power consumption, has been popularly used as a display equipment for image information and character information of an information equipment as represented by a personal computer, a portable information terminal, a portable telephone, a digital camera, and a visual equipment such as a camera-built-in type VTR equipment. Recently, along with spreading of large-capacity media or starting of BS digital broadcasting due to the advent of DVD and the rapid progress of large-capacity magnetic drives, the fusion of a personal computer and a video digital media is in progress and the demand for an image display device having high image quality which can cope with such an application is increased. A liquid crystal display adopting an in-plane switching (IPS) mode which applies a lateral electric field to liquid crystal sealed in a gap defined between upper and lower substrates has been recognized as a display method which is capable of satisfying such a demand for high image quality and various improvements have been made aiming at the further enhancement of the image quality.
On the other hand, along with spreading of portable telephones and portable information terminals, the demand for medium-sized or small-sized liquid crystal display devices which exhibit extremely small power consumption has been increased.
In the liquid crystal display device adopting the IPS mode, as disclosed in Japanese Patent Laid Open H07-36058, a method which performs switching of liquid crystal using a lateral electric field which is generated between two-layered metal electrodes sandwiching an insulation film therebetween has been most popularly used. A defect of such a structure lies in that, compared to a display device adopting a usual TN method, it is difficult to increase the numerical aperture of pixels so that the light utilization efficiency is low. Since it is necessary to increase the brightness of a backlight to compensate for this defect, as the whole LCD module, it is difficult to seek for the low power consumption which is demanded with respect to a notebook type personal computer or a portable terminal.